Thanks !

@Volker_E when will it be available in core? If I am developing an extension, should I load it in my extension folder (as an npm dependency, then copied into a folder), or should I wait for it to be available in core?

@JGirault Short answer: If you want to use it today, do it as you've said (dependency).
As it's a variables containing file, where the variable names are pretty stable it should be very easy to exchange it with core implementation any time soon. WMUI Base is also following Semantic Versioning, which gives a clear indication of possible breaking changes.
Long answer is connected to T112747